Hydrobiologia

https://doi.org/10.1007/s10750-020-04400-0 (0123456789().,-volV)( 0123456789().,-volV)

PRIMARY RESEARCH PAPER

Longitudinal river zonation in the tropics: examples of fish and caddisflies from the endorheic Awash River, Ethiopia

Gernot K. Englmaier . Daniel S. Hayes . Paul Meulenbroek . Yonas Terefe . Aschalew Lakew . Genanaw Tesfaye . Herwig Waidbacher . Hans Malicky . Alemayehu Wubie . Patrick Leitner . Wolfram Graf

Received: 28 March 2020 / Revised: 14 August 2020 / Accepted: 29 August 2020 Ó The Author(s) 2020

Abstract Specific concepts of fluvial ecology are differences in spatial species assemblage structure and well studied in riverine ecosystems of the temperate identified characteristic taxa of the observed bio- zone but poorly investigated in the Afrotropical coenoses by indicator species analyses. Fish and region. Hence, we examined the longitudinal zonation caddisfly assemblages were clustered into highland of fish and adult caddisfly (Trichoptera) assemblages and lowland communities, following the freshwater in the endorheic Awash River (1,250 km in length), ecoregions, but separated by an ecotone with highest Ethiopia. We expected that species assemblages are biodiversity. Moreover, the caddisfly results suggest structured along environmental gradients, reflecting separating the heterogeneous highlands into a forested the pattern of large-scale freshwater ecoregions. We and a deforested zone. Surprisingly, the Awash applied multivariate statistical methods to test for drainage is rather species-poor: only 11 fish (1 endemic, 2 introduced) and 28 caddisfly species (8 new records for Ethiopia) were recorded from the Gernot K. Englmaier and Daniel S. Hayes: equally contributing authors. mainstem and its major tributaries. Nevertheless, specialized species characterize the highland forests, Handling editor: Marcelo S. Moretti

G. K. Englmaier (&) Y. Terefe Institute of Biology, University of Graz, Universita¨tsplatz Department of Biological Sciences, Ambo University, 2, 8010 Graz, Austria P.O. Box 95, Ambo, Ethiopia e-mail: [email protected] A. Lakew Á G. Tesfaye Á A. Wubie D. S. Hayes Á P. Meulenbroek Á Y. Terefe Á EIAR-National Fisheries and Aquatic Life Research H. Waidbacher Á P. Leitner Á W. Graf (&) Center, P.O. Box 64, Sebeta, Ethiopia Institute of Hydrobiology and Aquatic Ecosystem Management (IHG), Vienna, University of Natural H. Malicky Resources and Life Sciences, Gregor-Mendel Straße 33, Sonnengasse 13, 3293 Lunz am See, Austria 1180 Vienna, Austria e-mail: [email protected]

D. S. Hayes Centro de Estudos Florestais (CEF), Instituto Superior de Agronomia, University of Lisbon, Tapada da Ajuda, 1349-017 Lisbon, Portugal

123 Hydrobiologia whereas the lowlands primarily host geographically At the same time, anthropogenic impacts on aquatic widely distributed species. This study showed that a ecosystems are rapidly increasing on a global scale combined approach of fish and caddisflies is a (Darwall et al., 2018; Sabater et al., 2018). The effects suitable method for assessing regional characteristics of deforestation, intensification of agriculture and of fluvial ecosystems in the tropics. other land-use changes, hydropower, river engineer- ing, and water pollution threaten aquatic biodiversity Keywords Africa Á Biodiversity Á Biogeography Á (e.g. Clausen & York, 2008; Fitzgerald et al., 2018; Species assemblages Á Freshwater ecoregions Á Hayes et al., 2018, 2019; Meulenbroek et al., 2019). Indicator species These trends can even have visible impacts on large- scale ecosystem processes (Darwall et al., 2018). The serial discontinuity concept was developed to address these pressures (Ward & Stanford, 1983, 1995). It Introduction suggests that dams and other anthropogenic stressors can disrupt the underlying natural gradient and cause In the early to mid-twentieth century, limnologists an upstream or downstream shift of species, as well as intensively described the longitudinal distribution of divide the river network into discrete zones. However, aquatic communities along rivers (e.g. Thienemann, natural influences such as lakes can also create 1925; Huet, 1949; Harrison & Elsworth, 1958; Illies, comparable patterns (Stanford et al., 1988). Hence, it 1961a, b; Illies & Botosaneanu, 1963). These studies is evident that, in contrast to the assumption of an enhanced the understanding of fluvial ecosystems, and uninterrupted gradient (Vannote et al., 1980), discon- the river continuum concept even became a frequently tinuities or transition zones constitute a significant tested hypothesis in applied fluvial ecology (Vannote component of faunal zonation (Statzner & Higler, et al., 1980). Since then, knowledge on riverine 1986). Moreover, certain functional process zones distribution patterns has been used, for example, to may repeatedly appear along a river and even form establish bioindication systems (e.g. Schmidt-Kloiber comparable patterns within an ecoregion. Beyond the & Hering, 2015) and river assessment criteria (e.g. ecoregional level, however, such patterns may be less Aarts & Nienhuis, 2003; Welcome et al., 2005). predictable (Thorp et al., 2006). Therefore, it must be Nevertheless, taxonomy and taxa differentiation of clarified if and to which extent zonation studies many biota, as well as their habitat preferences, conducted in tropical streams and rivers also reveal functional traits, and distribution patterns, are often such discontinuities reported for other systems still poorly understood (Balian et al., 2008). This is (Arau´jo et al., 2009), as well as if the ecoregion especially the case in tropical rivers (e.g. Gibon & regulates community zonation (Thorp et al., 2006). Statzner, 1985; Malicky & Chantaramongkol, 1993; Fish (Pisces) and caddisflies (Insecta: Trichoptera) Winemiller et al., 2008; Laudee & Prommi, 2011; are widely used to describe longitudinal changes of Skelton & Swartz, 2011; Ochieng et al., 2019). community structures (e.g. Harrison & Elsworth, Despite recent advances (Malicky & Chantara- 1958;Le´veˆque et al., 1983; Stanford et al., 1988). mongkol, 1993; Arau´jo et al., 2009), most conceptual These two organism groups provide the advantage of studies on river zonation were conducted in temperate relatively low sampling effort, the coverage of diverse regions of Europe and North America (Hawkes, 1975), habitat characteristics in the respective river stretches, which may limit the adoption of established concepts and a more profound taxonomic knowledge in com- into tropical regions (Arau´jo et al., 2009). Besides, the parison to other organism groups. Besides, both lack of knowledge of tropical rivers is a limiting factor groups have a high indicative power regarding envi- in assessing the integrity of these ecosystems. Hence, ronmental conditions. They are therefore implemented the scarcity of tropical studies impedes the assessment within the EU Water Framework Directive (2000/60/ of diversity and distribution patterns, as well as a EC) as faunistic biological quality elements to assess comparison to concepts and hypotheses of fluvial the ecological status of freshwater systems. Whilst fish ecology of temperate rivers (Ward et al., 2002; Thorp mostly respond to mesohabitat characteristics, caddis- et al., 2006). flies depend more on the availability of microhabitats. Particularly the latter is increasingly used for 123 Hydrobiologia ecological status assessment of African rivers (e.g. shared species of both adjacent communities should Dickens & Graham, 2002; Masese et al., 2009; Kaaya exist. et al., 2015; Lakew & Moog, 2015; Alemneh et al., 2019). However, ecological studies in riverine ecosys- tems of the Afrotropical region often rely on a high Materials and methods level of taxonomic resolution, such as family or genus level (e.g. Kaaya et al., 2015; Lakew & Moog, 2015; Study area and sampling sites Alemneh et al., 2019), despite the importance of including species-level information to enhance under- The Awash River catchment, with an area of standing of distribution patterns (Malicky & Chan- 112,696 km2, is home to approximately 14.9 million taramongkol, 1993). So far, however, species-specific people, making it one of the most important and studies throughout the Afrotropical realm mainly industrialized drainage basins in Ethiopia (Tesfaye & focused on taxonomy or a wide biogeographic context Wolff, 2014; Ministry of Environment, Forest and (e.g. Roberts, 1975) but rarely covered aquatic com- Climate Change, MEFCC, 2018). The Awash River munities in entire river systems (Harrison & Elsworth, springs in the Ethiopian Highlands at an altitude 1958; Payne et al., 2010). of [ 3,000 m. It flows for 1,250 km along the north- In this study, we explored the longitudinal zonation ern part of the Main Ethiopian Rift, where it finally of fish and adult caddisfly species in a long drains into saline Lake Abbe at the Ethiopian–Djibouti ([ 1,000 km, sensu Grill et al., 2019) tropical river border at an altitude of around 250 m (Tesfaye & in East Africa, including its major tributaries. We Wolff, 2014; Tadese et al., 2019). Most tributaries selected the Awash River in the Main Ethiopian Rift as originate in the highlands and join the mainstem river a case study because of several unique characteristics: from the West (Fig. 1). the river is an endorheic drainage which flows into the In the highlands, the mean annual precipitation Afar Depression, an arid region; it exhibits a distinc- amounts to 1,600 mm, and only 160 mm in the tive tectonic setting with a stepwise longitudinal and northern part of the catchment (Edossa et al., 2010). altitudinal gradient; and the drainage is subdivided Similarly, the mean annual air temperature exhibits a into two freshwater ecoregions, the Ethiopian High- spatial variation from 16.7 to 34.5°C (Keraga et al., lands and the Northern Eastern Rift (Abell et al., 2019). The drainage basin consists of two freshwater 2008). Our overall objective was to describe longitu- ecoregions: the Ethiopian Highlands and the Northern dinal zonation patterns of the fish and caddisfly Eastern Rift (Abell et al., 2008). assemblages in the Awash River drainage by provid- To study the distribution of the fish and caddisfly ing species-level information as the most reliable basis fauna, we sampled the Awash River from the source for assessment. By using a combined approach of fish, region in the Chilimo Forest to the lakes in the Afar adult caddisflies, and environmental variables, we Depression, as well as seven of its tributaries, draining aimed to answer the following questions: How are fish the southern slopes of the Ethiopian Highlands into the and caddisfly species distributed longitudinally along Main Ethiopian Rift (Fig. 1; Table 1). We selected a a tropic endorheic river and its major tributaries? Can total of 24 sampling sites (16 in the Awash River and 8 distinct species assemblages be distinguished, and, if in the tributaries) based on habitat criteria (natural yes, which environmental parameters are crucial in riparian vegetation, diverse meso- and microhabitat steering community composition in the dry season? structures), tectonic setting (geomorphological char- Besides, we wanted to know if both organism groups acteristics), minimal direct anthropogenic impact, and show the same distribution and grouping pattern. accessibility (see Englmaier, 2018). The accessibility Moreover, to assist in improved river management, we of river stretches was restricted by the permission of aimed to detect indicator species characteristic of the local authorities, dense riparian vegetation, physiog- observed biocoenoses. Based on theoretical concepts, raphy, water depth, or the presence of abundant we expected that species assemblages are structured crocodiles. along environmental gradients and reflect the pattern Sites S1–5 (Awash) and T8 (tributary) are located of large-scale freshwater ecoregions. Accordingly, in the Ethiopian Highlands freshwater ecoregion transition zones between discrete biocoenoses with (Abell et al., 2008). These river stretches are usually 123 Hydrobiologia

38.0 °E 39.0 °E 40.0° E 41.0 °E 42.0 °E 43.0 °E 44.0° E 13.0 °N 440 YEMEN 523 N ERITREA 527 439 ETHIOPIA 526 528 12.0 °N 525 529 522 Gulf of Aden Mille R. S14 S15

525 T1 S16 530 531 DJIBOUTI S13 T2 Abbe L. 11.0 °N 521 1:28 000 000 T3 Awash R. 0 km 60 120 Borkana R. T4 SOMALIA T5 S12 Blue Nile R. T6 Yardi L. 10.0 °N Awash T7 Gotta R. catchment

S11

S1 a R. T8 Germam S2 9°N.0 Akaki R. Beseka L. S10 S3 S4 Omo R. Mojo R. S9 S8 S7 S5 S6

Meki R. Koka Reservoir

8°N.0

Ziway L. Abijata L. Wabe Shebelle R. Langano L. Shala L.

Fig. 1 Map of the study area, location of sampling sites (S1–16, Lake Victoria Basin, 522 Upper Nile, 523 Lower Nile, 525 T1–8), dams (red lines), and the cascades at Awash Kunture Ethiopian Highlands, 526 Lake Tana, 527 Western Red Sea (blue line). Numbers in the overview map of the Horn of Africa Drainages, 528 Northern Eastern Rift, 529 Horn of Africa, 530 refer to the following freshwater ecoregions (Abell et al., 2008): Lake Turkana, 531 Shebelle-Juba 439 southwestern Arabian Coast, 440 Arabian Interior, 521 characterized by steep gradients, coarse stony sub- 2018). The riverbed consists either of bedrock or sand. strate (macrolithal to microlithal, see Table 1), and a In contrast, the tributary sites (T1–7) are characterized confined river course (Englmaier, 2018). With the by a wide river corridor and coarse substrate (Table 1). exception of the protected Chilimo Forest (S1, In the Northern Eastern Rift, the longitudinal gradient National Forest Priority Area), the region is subject of the Awash River is interrupted by three hydroelec- to extensive anthropogenic impacts with intensive tric power plants (Koka Reservoir, Awash II–III) and agricultural use and overgrazing by livestock, result- one irrigation dam (Tendaho Reservoir). At Metahara ing in the loss of natural vegetation (Tafere et al., (downstream of S9), the saline Lake Beseka is 2013; Kebede et al., 2020). artificially connected to the Awash River (Fig. 1). The remaining sites are situated in the Northern Eastern Rift freshwater ecoregion (Abell et al., 2008). Field work Here, the Awash River flows through alternating steep and low gradient sections with sequences of confined We sampled sites during low flow conditions in the dry river stretches and extensive wetlands (Englmaier, season over a time frame of 3 years (Table 1). At each 123 Hydrobiologia 0.1 0.6 1.0 0.4 0.4 2.1 1.1 0.8 0.2 0.3 0.1 0.1 0.3 0.1 3.6 1.1 0.2 1.8 0.5 1.2 2.2 0.8 0.7 0.5 l- ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± C) ° Water temper- ature ( ) 1.5 28.5 3.231.8 20.6 20.3 37.0 21.1 75.2 24.2 26.8 21.1 5.46.2 29.2 30.2 28.4 34.2 5.2 26.2 5.1 21.5 12.4 24.9 2.1 30.0 34.6 24.2 22.5 20.4 8.2 21.5 11.2 24.6 15.3 15.9 23.2 26.1 17.4 29.0 7.6 31.9 4.3 31.2 9.411.8 30.0 24.8 1 - ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± Scm l Conductivity ( 0.7 580.2 0.01.1 284.7 0.4 346.3 0.1 360.0 0.4 540.3 286.7 0.30.5 697.4 692.8 1.0 1,509.6 0.2 570.2 0.1 349.7 0.0 1,206.3 0.1 853.5 0.4 851.3 0.7 345.3 0.1 308.7 0.0 941.3 0.1 243.9 0.1 975.3 0.2 1,710.3 0.2 550.4 0.1 715.1 0.50.4 410.8 510.0 ) 1 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± - DO (mg cm 1.4 7.0 0.218.0 7.5 6.4 6.1 2.6 7.3 1.7 8.6 7.3 1.10.8 7.8 7.0 8.62.4 11.4 7.2 0.2 8.3 0.6 4.9 0.5 7.2 3.7 7.8 0.8 8.7 1.2 7.9 0.5 8.1 2.2 7.3 0.1 5.6 0.7 7.3 7.3 7.4 2.4 5.9 1.60.5 11.9 10.1 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± (%) 0.4 114.6 0.2 107.8 0.00.1 85.7 103.4 0.1 124.1 0.2 97.7 0.0 110.8 0.1 98.4 0.3 183.1 0.0 105.1 0.0 109.8 0.0 65.1 0.2 100.0 0.1 103.4 0.1 126.3 0.1 103.4 0.0 106.4 0.1 95.7 0.1 75.0 0.2 101.5 0.3 104.6 0.0 94.0 0.5 178.2 0.1 142.5 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± Water parameters Slope pH DO E 0.04 8.7 E 0.00E 9.5 0.12 8.7 E 0.12E 8.7 1.24E 1.07 9.3 9.1 E 2.20 9.8 EE 0.64E 1.24 8.7 E 1.32 8.5 E 0.20 8.7 0.16 8.7 8.6 EE 0.18 0.10 8.7 8.5 EE 1.13 1.20 9.4 8.8 00 00 00 00 00 00 00 E 0.74E 8.8 0.12E 8.5 0.42 8.2 E 1.43 9.1 00 00 00 00 00 00 00 00 00 E 1.08 8.8 E 0.76E 8.7 0.58 8.8 00 00 43 00 51 37 57 54 13 16 00 00 44 18 58 30 43 00 00 3 23 47 44 36 0 0 0 0 0 0 0 E 4.84 8.4 7 10 3 19 44 0 0 0 0 0 0 0 0 0 0 00 58 0 0 0 0 0 41 34 7 38 45 55 57 58 9 23 36 37 54 12 46 23 58 0 51 ° ° ° ° ° ° ° ° 0 6 33 38 10 10 55 ° ° ° ° ° ° ° ° ° 8 ° ° ° ° ° ° ° N, 40 N, 41 N, 41 N, 40 N, 39 N, 39 N, 39 N, 39 N, 38 N, 38 N, 38 N, 38 N, 39 N, 40 N, 41 N, 39 N, 39 00 00 00 00 00 00 00 00 N, 38 N, 39 N, 39 N, 40 N, 40 N, 38 00 00 00 00 00 00 00 00 00 N, 38 00 00 00 00 00 53 50 5 50 50 10 09 14 21 00 00 39 21 56 16 23 2 9 6 48 50 42 0 0 0 0 0 0 0 0 0 1 23 59 24 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 38 35 30 13 41 7 06 31 20 5 24 4 42 39 23 28 30 57 5 4 51 33 20 2 ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° Geographic coordinates b Freshwater ecoregion Distance from source (km) Altitude (m a.s.l.) a C 1,417 NER 10 period C 1,902 NER 11 River River Sampling site characteristics S1 Chilimo Forest A 2,389 5 EH 9 T3 Middle Borkana S4S5S6S7 AwashS8 Kunture Sulula Lafessa A Wonji Korkada 2,003 A AS15 110 A AS16 1,916 1,608 EH 1,552 1,260 128 Asaita 205 Lake Gamari 246 EH 8 311 NER C NER NER C 8 8 T7 8 338 8 362T8 1,159 1,103 Robit River NER Akaki NER River C 11 11 C 1,367 2,429 NER EH 9 9 S10S12 YimreS14 Kada Bada Dubti B B 797 570 C 457 738 378 NER NER 1,069 9 NER 10 11 S3 Awash BeloS9 AS11 2,065 Nur Sada Worer 73 B EH B 1,214 8 328 743 NER 507 NER 8 9 S2 Gare Arera A 2,244 14 EH 9 S13 AdayituT2 CT4 Upper Borkana T5 460T6 926 Jara River Ataya River Yewuha NER River C C C 11 1,434 1,436 1,138 NER NER NER 10 10 10 T1 Lower Mille River C 482 NER 11 Awash River Awash River 0510152035105 5 10 20 25 25 15 Tributaries Site ID Name Survey Table 1 Sampling site characteristics Substrate (%) Pelal Psammal Akal Microlithal Mesolithal Macrolithal Megalithal 123 123 Table 1 continued Substrate (%) Pelal Psammal Akal Microlithal Mesolithal Macrolithal Megalithal

5202530155 0 51510105 5 50 0 10 5 5 5 40 35 56015155 0 0 30 40 15 5 5 5 0 0 10 5 0 0 15 70 15 25 15 10 10 10 15 0152030205 10 50 30 10 5 0 0 5 20 55 20 5 0 0 0 5 35 15 5 10 15 15 15 30 5 5 10 20 15 30 60 5 5 0 0 0 10 70 15 5 0 0 0 Tributaries 5 20 5 20 20 20 10 015151530205 15 5 5 5 20 30 20 0 10 5 15 20 30 20 0 5 10 20 45 15 5 5 5 10 10 35 20 15 515151030205 30 5 0 0 20 25 20 aSurveys conducted during dry season in three periods: A, November and December 2017 (beginning of dry season); B, January 2018 (middle of dry season); C, March 2019 (end of dry season) bFreshwater ecoregions according to Abell et al. (2008), EH Ethiopian Highlands, NER Northern Eastern Rift cWater parameters given as mean ± SD Hydrobiologia Hydrobiologia ocation, we investigated a representative stretch with a African caddisflies in general (e.g. Scott, 1975; Terefe length between 500 and 1,000 m. In order to link fish et al., 2018; Ochieng et al., 2019). Only 105 larval and caddisfly presence to abiotic variables, we stages of 747 Sub-Saharan species of African caddis- recorded different water parameters. We measured flies were known by the early 1980s (Scott, 1983). dissolved oxygen concentration (%, mg cm-1), con- Since then, only twelve additional studies have ductivity (lScm-1), pH, and water temperature (°C) produced descriptions of larvae for individual species with a portable HACH-multimeter (HQ40d) at noon in (e.g. Malicky, 1994; Allaya, 2003; Ogbogu, 2008; three consecutive measurement series (three replicates Ogbogu & Okeze, 2008; Terefe et al., 2018). each). The probes were placed in swift current (10 cm We collected adult stages of caddisflies from the sub-surface) at three different points (each 20 m apart) riparian zone with sweep nets (at dusk for 30 min, without prior disturbance of the upstream reach. In mesh size 1 mm) and light traps. The traps consisted of addition, we classified dominating substrate types: a fluorescent tube (15 W Blacklight blue tube) pelal, psammal, akal, microlithal, mesolithal, macro- attached upon a rectangular pan (40 9 25 9 7 cm), lithal, and megalithal (Moog et al., 1999). We half-filled with water, and containing detergent to recorded geographic coordinates and altitude of each reduce the surface tension. The exposure time of light sampling site with a Garmin VISTA e-trex GPS- traps was 60 min, starting from sunset. At each site, system. The distances from the source and slopes of we used one light trap. We fixed caddisfly samples in the sampling sites were obtained from Google Earth’s 95% ethanol for morphological identification. digital elevation model (Google Earth Pro v.7.3). No caddisfly samples were obtained from S9, S16 We collected fish from the main river channel, side (main channel), T4–6, and T8 (tributaries) due to local arms, and the shoreline of lakes. Sampling points restrictions. These sites were therefore excluded from included the following mesohabitats: riffles, runs, the analyses. pools, backwaters, woody debris piles, shoreline Reference material was stored in the collections of vegetation, undercut banks, gravel banks, and inshore the National Fisheries and Aquatic Life Research areas of lakes. Fishing effort was limited to Centre, Sebeta, Ethiopia (fish and caddisflies), the 100–120 min of active fishing and 2–9 h of passive Natural History Museum Vienna, Austria (fish), as exposure of gillnets and longlines (where applicable). well as the research collections of H. Malicky (Lunz Wadable stretches were sampled using a back-pack am See, Austria), W. Graf (University of Natural electrofishing unit (Honda GXV 50, direct current Resources and Applied Life Sciences, Vienna, Aus- 1.5 kW, 300/580 V), seine nets (mesh size 1.5 mm), tria) and the Senckenberg Research Institute and and frame nets (mesh size 1.5 mm). In deeper waters, Museum of Nature (SMF, Frankfurt am Main, Ger- fish were collected with gill nets (mesh sizes 80 mm many) (caddisflies). and 60 mm), cast nets (mesh size 15 mm), and longlines. Most fish specimens were identified in the Species identification field and released back to the river. A subsample from each locality, including all species and morphotypes, All species were identified as morphospecies based on was taken for detailed morphological examination. external morphological and meristic traits. The fol- These specimens were first anesthetized with etheric lowing available literature was used for fish identifi- clove oil diluted in water and later fixed in 6–10% pH cation: Getahun (2000), Golubtsov et al. (2002), neutral formalin or 95% ethanol. Stiassny & Getahun (2007), Habteselassie et al. Regarding macroinvertebrates, we chose caddis- (2010), Habteselassie (2012), and Moritz et al. flies as an indicator group since, aside from their (2019). Caddisfly identification was based on Tobias elaborate adult taxonomy, they represent a spectrum of & Tobias (2008) and the reference collections of the the community that can be attracted and documented authors, with the assistance of Franc¸ois-Marie Gibon. by light traps. By targeting adult caddisflies, we aimed Direct comparison to museum samples (type speci- at reducing insufficient results due to methodological mens, comparative material) included specimens in problems in benthic sampling (e.g. limited accessibil- the collections of the Natural History Museum ity of the entire habitat mosaic of a given site) and due (BMNH, London, England), the Muse´um National to the low knowledge level on larval taxonomy of D’Histoire Naturelle (MNHN, Paris, France), SMF, 123 Hydrobiologia and the research collections of H. Malicky and W. species for the observed biocoenoses of different river Graf. sections by conducting an indicator species analysis For polymorphic fish groups (Garra, Labeobar- (Dufreˆne & Legendre, 1997) with PC-ORD v.5.33 bus), we followed the group subdivision of Englmaier (McCune & Mefford, 2006). Based on 308 random- (2018), which was based on the comparison of 500 bp izations and 4,999 permutations, only species with an of the mitochondrial CO1 gene, with the following indicator value (IV) of C 40 and P \ 0.05 (Monte clarifications: Garra sp. was identified as Garra Carlo permutation test) were considered significant. makiensis based on the comparison with syntypes at The indicator analysis was based on presence/absence BMNH; G. aff. makiensis was identified as Garra data. Group membership of sampling sites was based aethiopica based on the comparison with syntypes at on the results of the CA. For all tests, we considered MNHN; Labeobarbus cf. intermedius was identified P \ 0.05 as significant. on species level based on the comparison with the holotype at SMF and the genetic analyses of Beshera & Harris (2014); and L. cf. nedgia (the sympatric Results ‘‘lipped’’ form of L. intermedius) was provisionally included in L. intermedius. Faunal characteristics For information on the author and year of descrip- tion of the identified species, the reader is referred to We recorded a total of 10,111 fish specimens (11 Tables 2 and 3. species, 4 families) and 23,757 adult caddisflies (28 species, 7 families). Of the 11 fish species, 9 are native, Data analyses and 2 introduced (Cyprinus carpio, Coptodon zillii). Fish species of the family Cyprinidae (three genera, We explored patterns in fish and caddisfly assemblage five native species, one introduced species) showed structure and distribution through a multivariate the most dominant occurrence (Table 2). Of these, the analysis approach. We analyzed the data based on genera Garra (three species) and Labeobarbus (two species presence/absence instead of using relative species) were widely distributed throughout the entire abundances to avoid a systematic bias due to unequal drainage system. At species level, L. intermedius was sampling methods. For each organism group and a most widespread, with a continuous distribution from combined dataset (fish and caddisflies), we performed S5 to S16 (1,916–338 m) but absent from sampling two-way cluster analyses [CA, using the Jaccard sites above the cascades at Awash Kunture (upstream coefficient and flexible beta linkages (- 0.25)] and of S5). At a few sites (S5, S9–10, and T4), predom- non-metric multidimensional scaling (NMDS, using inantly over coarse substrate, we found the sympatric the Jaccard coefficient) to explore and visualize ‘‘lipped’’ form of L. intermedius. Garra dembeensis patterns of similarity in the datasets. Both methods was the only species present in both, the source region were implemented in PC-ORD v.5.33 (McCune & in the Chilimo Forest (S1, 2,389 m) and the Lower Mefford, 2006). Group circumscription in NMDS was Awash (S14, 378 m) but showed a highly fragmented based on individual CA, with subdivisions supported distribution restricted to riffles over a stony substrate. by 37.5% total information used. Garra aethiopica and Enteromius yardiensis showed Based on the above exploratory tools, we tested the the most restricted distributions. Whilst the former assemblage structure with a permutational multivari- inhabited river stretches [ 1,138 m, the latter was ate analysis of variance (PERMANOVA; Anderson, found only in lower reaches of the main river channel 2001), with 999 permutations implemented in the R and aquatic floodplain habitats (S12–16, 570–338 m). package vegan (Oksanen et al., 2015) in R v.3.4.3 (R Collections of caddisflies (Table 3) mainly com- Core Team, 2017). prised the families Leptoceridae (7 genera, 11 The identification of indicator species is imperative species), Hydropsychidae (3 genera, 8 species), for the classification and assessment of the ecological Ecnomidae (1 genus, 3 species), and Hydroptilidae integrity of a river ecosystem. As species-specific (2 genera, 3 species). A single species was found in bioindicators are rare or absent in most of the each of the remaining families (Dipseudopsidae, Afrotropical region, we determined characteristic Lepidostomatidae, and Polycentropodidae). In total, 123 Hydrobiologia

Table 2 List of fish species present in the Awash River drainage Family and species Authority Awash River Tributaries S1 S2 S3 S4 S5 S6 S7 S8 S9 S10 S11 S12 S13 S14 S15 S16 T1 T2 T3 T4 T5 T6 T7 T8

CICHLIDAE (1) Oreochromis (Linnaeus, 1758) X X X X X X XXXXXX X X niloticus (2) Coptodon zilliia (Gervais, 1848) X X CLARIIDAE (3) Clarias (Burchell, 1822) XXXXX X XXXXXX X X gariepinus CYPRINDAE (4) Garra (Pellegrin, 1927) X X X X X X X X X X X X aethiopica (5) Garra (Ru¨ppell, 1835) X X X XXXXXX X X XXXXXXXX dembeensis (6) Garra (Boulenger, 1903) XXXXX X XXXXXX XX makiensis (7) Labeobarbus (Ru¨ppell, 1835) X X X X X X X X X beso (8) Labeobarbus (Ru¨ppell, 1835) XXXXXX X XXXXXX XXXXX intermedius (9) Enteromius Englmaier, Tesfaye XXX X yardiensis & Bogutskaya, 2020 (10) Cyprinus Linnaeus, 1758 X X X X carpioa POECILIIDAE (11) Micropanchax (Vinciguerra, 1883) X X X X X X X X X X antinorii aIntroduced species 123 123 Table 3 List of caddisfly (Trichoptera) species present in the Awash River drainage Family and species Authority Awash Rivera Tributariesa S1 S2 S3 S4 S5 S6 S7 S8 S9 S10 S11 S12 S13 S14 S15 S16 T1 T2 T3 T4 T5 T6 T7 T8

ECNOMIDAE (1) Ecnomus nyab Mosely, XXXX 1948 (2) Ecnomus similis Mosely, XXXXX 1932 (3) Ecnomus thomasseti Mosely, XX XX 1932 DIPSEUDOPSIDAE (4) Dipseudopsis capensis Walker, X XXXX 1852 HYDROPSYCHIDAE (5) Amphipsyche (Brauer, X XXX XX X senegalensis 1875) (6) Cheumatopsyche afra (Mosely, XXXXXXXX X 1935) (7) Cheumatopsyche Martynov, XX XXXXXX XX X columnatab 1935 (8) Cheumatopsyche (Ulmer, XX XXXX X XX falcifera 1930) (9) Cheumatopsyche massa Malicky & XXX X X XX X Graf, 2012 (10) Cheumatopsyche (Ulmer, X sexfasciata 1904) (11) Cheumatopsyche Malicky & X themaz Graf, 2015 (12) Hydropsyche Kimmins, X abyssinica 1963 HYDROPTILIDAE (13) Hydroptila cruciatab Ulmer, 1912 X X X X X X (14) Hydroptila sp. X (15) Orthotrichia tharielb Malicky & XXXXX X X X XXX X Hydrobiologia Graf, 2015 LEPIDOSTOMATIDAE (16) Lepidostoma scotti Ulmer, 1930 X Table 3 continued Hydrobiologia Family and species Authority Awash Rivera Tributariesa S1 S2 S3 S4 S5 S6 S7 S8 S9 S10 S11 S12 S13 S14 S15 S16 T1 T2 T3 T4 T5 T6 T7 T8

LEPTOCERIDAE (17) Athripsodes fissus (Ulmer, X 1912) (18) Oecetis armaros Malicky & X Graf, 2015 (19) Oecetis reticulatellab Kimmins, XXX XXX XX 1957 (20) Oecetis tripunctata (Fabricius, XXX 1793) (21) Oecetis sp. X (22) Setodes squamosus Mosely, XX 1931 (23) Tagalopsyche Kimmins, XX aethiopica 1963 (24) Triaenodes serratusb Ulmer, 1912 X X X (25) Trichosetodes Kimmins, XX tjonnelandi 1963 (26) Trichosetodes Kimmins, X truncatus 1963 (27) Parasetodes sp. (near XXXX X X to P. respersellus) POLYCENTROPODIDAE (28) Nyctiophylax Jacquemart, X armigerab 1961 aSampling sites without collections of adult caddisflies: S9, S16, T4, T5, T6, T8 bNew species records for Ethiopia 123 Hydrobiologia

(a) (b)

Information Remaining (%) Information Remaining (%) S1 1.5 S1 1.5 100 75 50 25 0 100 75 50 25 0 S2 S1 S1 S3 t1 T2 S4 S3 1.0 S2 S2 S3 1.0 S2 f1 S3 T7 1 9 T1 T2 S4 S5 S4 10 S5 1 0.5 S5 T2 t2 8 S5 T7 T3 S6 0.5 T7 4 S7

9 2 S6 S8 s S4 S8 4 i 0.0 10 8 S7 x S10

Axis 2 A T3 3 S11 0.0 S14 S8 S6 S12 t3 S13 S10 -0.5 S7 6 S15 S10 2 3 S11 S13 6 7T1 S6 S13 7 S11 -0.5 2 S15 f2 S12 S14 S7 S14 S12 -1.0 T3 S8 T3 Ethiopian Highlands S14 Ethiopian Highlands S15 T1 S11 S12 S13 T2 t4 Final Stress = 4.85 S10 Final Stress = 16.13 -1.0 S15 T1 -1.5 T7 -1.5 -1.0 -0.5 0.0 0.5 1.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 Axis 1 Axis 1

Fig. 2 Non-metric multidimensional scaling (NMDS) dendro- based on individual CA, with subdivisions supported by 37.5% gram and two-way cluster analysis (CA) showing zone total information—dashed line. Environmental variables used as membership for a fish species assemblages and b adult caddisfly following: 1 slope, 2 conductivity, 3 water temperature, 4 species assemblages, based on presence/absence data and dissolved oxygen, 5 pH, 6 %pelal, 7 %psammal, 8 %microlithal, environmental variables. Group circumscription in NMDS is 9 %mesolithal, 10 %macrolithal

27 species were recorded in the main river. We only Faunal assemblages and zonation collected adult caddisflies at four tributary sites; all of the nine species found occurred in the Awash River, The dataset to assess faunal assemblage and zonation except for Hydroptila sp., which was detected only in patterns consisted of species presence/absence data for the Robit River (T7). Lepidostoma scotti, 9 fish species (2 non-native species were excluded) Cheumatopsyche themaz, and Oecetis armaros were and 28 caddisfly species (Tables 2, 3), 5 environmen- found exclusively in the Chilimo Forest (S1) and were tal parameters (slope, conductivity, water temperature, also absent from the upper tributary reaches (T2–3 and dissolved oxygen, pH) and dominating substrate types T7, above 1,367 m). Hydropsyche abyssinica, Oecetis (pelal, psammal, akal, microlithal, mesolithal, macro- tripunctata, Setodes squamosus, Tagalopsyche aethio- lithal, megalithal) (Table 1). pica, Triaenodes serratus, Trichosetodes tjoen- Overall, both fish and caddisfly assemblages nelandi, and Nyctiophylax armigera showed a showed distinct patterns along the longitudinal gradi- restricted distribution around the wetland area of the ent of the Awash River (Figs. 2, 3; Table 4). Koka Reservoir (S6–7). Orthotrichia thariel was the Regarding fish, NMDS and CA revealed a clear most widely distributed caddisfly species in the Awash separation of the Awash River between sites in the drainage and was found at an altitude range of Ethiopian Highlands and the Northern Eastern Rift 2,003–378 m. Amphipsyche senegalensis and Dipseu- (Fig. 2a; Table 4). The difference resulted from the dopsis capensis were recorded from the main channel absence of G. aethiopica downstream of S6 and the of the Awash at altitudes below 1,552 m. They were upstream limit of G. makiensis, Clarias gariepinus, absent from the tributaries, except for the Borkana and Micropanchax antinorii at the same site. The River at T3 (1,417 m). The two species of Hydroptila tributaries grouped within similar faunal assemblages (one hitherto undescribed) were most characteristic of the main river but did not follow the classification of for some of the tributaries (T1–3, T7, 1,902–482 m) freshwater ecoregions. Whilst G. aethiopica, G. and also found at S8 and S14 in the main channel dembeensis, and Labeobarbus beso were dominant (Table 3). in the Upper Borkana River (T2, 1,902 m) and Robit River (T7, 1,367 m), we found typical lowland species in the Lower Mille River (T1, 482 m) and the Middle Borkana River (T3, 1,417 m) (Table 2).

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* Caddisfly species presence absence Information Remaining (%) 100 75 50 25 0 S1S2 S3 S4 S5 T2 T7 S6 S7 S8 S10 S11S12 S15 S13 S1 4 T3 T1 (a) (b) C .* themaz 1.5 Information Remaining (%) L.* scotti O.* armaros 100 75 50 25 0 G. aethiopica S2 C .* massa S3 S1 L. beso C .* afra S1 T2 S2 1.0 C .* falcifera S3 c1 G. dembeensis S4 Othariel.* T7 H .* cruciata 1 9 S5 Enya.* S5 T2 E.* similis 0.5 H .* abyssinica S4 T7 O .* tripunctata T.* serratus 8 10 S6 c2 S .* squamosus 5 S7 T.* aethiopica Axis 2 T.* tjonnelandi 4 S8 0.0 N.* armigera T1 S10 G. makiensis C. gariepinus S8 T3 3 S11 S13 L. intermedius S12 O. niloticus S6 C .* columnata 6 S14 S15 -0.5 7 2 c3 M. antinorii S7 S13 O.* reticulatella S10 A. senegalensis* Ethiopian Highlands S12 S14 Parasetodes sp.* S15 T3 E . yardiensis Final Stress = 11.18 D .* capensis -1.0 S11 T1 E.* thomasseti C .* sexfasciata -1.5 -1.0 -0.5 0.0 0.5 1.0 Hydroptila sp.* Axis 1 A.* fissus Oecetis sp.* T.* truncatus

Fig. 3 Non-metric multidimensional scaling (NMDS) dendro- two-way cluster analyses (37.5% information retained—dashed gram and two-way cluster analysis showing zone membership line). Environmental variables used as following: 1 slope, 2 for a a combined dataset of fish and caddisfly species and b two- conductivity, 3 water temperature, 4 dissolved oxygen, 5 pH, 6 way cluster analyses showing characteristic assemblages along %pelal, 7 %psammal, 8 %microlithal, 9 %mesolithal, 10 the river gradient. Group circumscription is based on individual %macrolithal

In contrast to fish, the analyses of adult caddisfly clearly distinguished from species assemblages further assemblages showed a more detailed assemblage downstream by G. aethiopica, L. beso, C. massa, C. structure with four statistically distinct groups afra, C. themaz, L. scotti, and O. armaros. Altitude (Fig. 2b; Table 4). In detail, the first three sites ranged from 2,389 to 1,608 m, dissolved oxygen was (S1–3, [ 2,065 m) were distinct, with Cheumatopsy- close to saturation (mean 103.8%), water temperature che afra and Cheumatopsyche massa common to all ranged from 15.9 to 21.1°C, and conductivity was locations, but L. scotti, C. themaz, and O. armaros between 234.9 and 360.0 lScm-1. A sharp increase in restricted to the Chilimo Forest (S1). Sites S4 and S5 water temperature (15.9–20.4°C) and conductivity of the Ethiopian Highlands freshwater ecoregion (243.9–345.3 lScm-1) was recorded between S1 and grouped with S6–8 of the Northern Eastern Rift S2, which were 9 km apart (Table 1). All sampling region. Ecnomus nya, Ecnomus similis, T. serratus, sites in the Upper Awash zone were characterized by a and O. tripunctata were most characteristic for this coarse substrate (microlithal to megalithal). Only at river stretch. The assemblage structure further down- site S3 (Awash Belo), the riverbed consisted of a high stream was dominated by D. capensis, A. senegalensis, percentage of psammal (20%) and akal (25%). and Parasetodes sp. The fourth group, consisting of Sites S6–8, located in the Northern Eastern Rift, the tributaries (T1–3, T7), was separated from the form a transition zone (approximately 123 km in main river (except for S14) by Hydroptila cruciata and length) from the mountains to the lowlands. Here, we Hydroptila sp. recorded the highest species richness (nine fish and 20 For the combined dataset of fish and caddisflies, the caddisfly species) (Fig. 3b; Tables 2, 3). The distri- NMDS and CA revealed three distinct zones (Fig. 3), bution of some caddisfly species (Cheumatopsyche which were statistically significant (Table 4). Sam- sexfasciata, H. abyssinica, O. tripunctata, S. squamo- pling sites S1–5 from the Ethiopian Highlands, sus, T. aethiopica, T. serratus, Trichosetodes tjon- including T2 and T7 from the Northern Eastern Rift, nelandi, and N. armigera) was even restricted to this form a separate but heterogeneous cluster. The Upper stretch, ranging from an altitude of 1,608 to 1,214 m. Awash, with a length of approximately 205 km, was Surprisingly, no fish species was particularly

123 Hydrobiologia

Table 4 PERMANOVA results based on Jaccard dissimilarity using presence/absence data for species assemblage structures using three datasets (fish, caddisflies, and both groups combined) Factor df Sum Sq R2 FP

Fish Zones 1 2.738 0.793 61.384 0.001 Residuals 16 0.714 0.207 Caddisflies Zones 3 3.094 0.571 6.209 0.001 Residuals 14 2.325 0.429 Combined Zones 2 2.470 0.550 9.154 0.001 Residuals 15 2.024 0.450 Degrees of freedom (df), sum of squares (Sum Sq), (R2), F-ratios, and P-values for the river zones (zones referring to those in Figs. 2, 3a) characteristic for this zone. The fish fauna included conductivity (349.7–1,206.3 lScm-1), followed by a typical lowland elements such as G. makiensis, C. decline to 692.8 lScm-1 (S15). The highest conduc- gariepinus, and M. antinorii. Garra aethiopica (typ- tivity measurement in the Awash drainage was ical for the Upper Awash) was still present at S6 but recorded in Lake Gamari (1,710.3 lScm-1). In the disappeared further downstream. In this transition Lower Awash, pelal, psammal and microlithal were zone, dissolved oxygen was close to saturation (mean the dominant substrate types. 108.4%, max. 124.1% at S6). Water temperature Faunal assemblages in the main river were not ranged from 21.1°C (S7) to 24.2°C (S6), and conduc- always comparable to those found in tributaries. The tivity was between 286.7 lScm-1 (S7) and 540.3 lS latter often showed limited species numbers, espe- cm-1 (S6). Upstream of Koka Reservoir, both water cially for caddisflies (Fig. 2b). Besides, the tributaries temperature and conductivity showed a sharp increase showed a different substrate composition and a (21.1–24.2°C and 360.0–540.3 lScm-1, respectively) substantially higher water temperature with up to followed by a notable drop below the dam 34.2°C at T6 (Yewuha River, 1,138 m) (Table 1). (24.2–21.1°C and 540.3–286.7 lScm-1, respectively) Similar to the analyses of the fish dataset, the (Table 1). The dominant substrate ranged from psam- combined CA grouped the tributary stretches within mal (S6–7) to megalithal (S8). the faunal zones of the main river (Fig. 3). Tributaries At altitudes below 1,214 m, the Lower Awash T2 (Upper Borkana River, 1,902 m) and T7 (Robit (approximately 922 km in length) was dominated by River, 1,367 m) fall within the Upper Awash, and T1 widely distributed fish species such as G. makiensis, C. (Lower Mille River, 482 m) and T3 (Middle Borkana gariepinus, Oreochromis niloticus, M. antinorii, L. River, 1,417 m) cluster with the Lower Awash. intermedius, and E. yardiensis (S12–16). Characteris- tic caddisfly species in this zone were D. capensis, A. Indicator species senegalensis, Cheumatopsyche columnata, and Parasetodes sp. In comparison to the two other zones, We found that, in the Awash River, distinct species dissolved oxygen concentration in the Lower Awash reflect the biocoenotic separation reported above was lower on average (mean 92.6%, range (Figs. 2, 3; Tables 2, 3). 65.1–110.8%), whereas water temperature was con- The individual analysis for fish species allowed us sistently high ([ 24°C) with a mean temperature of to distinguish two groups along the boundaries of the 27.5°C. Similarly, conductivity exhibited the highest freshwater ecoregions. Garra aethiopica and L. beso values in the Lower Awash, ranging from 692.8 to were most characteristic for mainstem sites in the 1,206.3 lScm-1 (mean 894.4 lScm-1). Between Ethiopian Highlands (S1–5) and two tributaries (T2, sites S9 and S11, we recorded a sharp increase in T7). In the Northern Eastern Rift, G. makiensis, L.

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Table 5 Indicator species analysis results for fish (f), caddis- maximum indicator value (IV) for each species, based on 308 flies (t) and the combined (c) dataset (fish and caddisflies): randomisations and 4,999 permutations (see Dufreˆne & Monte Carlo permutation test of significance of observed Legendre, 1997) Species Zonea IV Mean SD P Species Zonea IV Mean SD P

Fish Combined Garra aethiopica f1 91.7 33.4 10.09 0.0010* Garra aethiopica c1 75.0 32.0 10.65 0.0012* Garra dembeensis f1 61.1 48.2 6.22 0.1126 Garra dembeensis c1 40.0 38.4 4.64 0.5903 Garra makiensis f2 100 41.6 8.56 0.0002* Garra makiensis c2 50.0 35.4 9.78 0.0230* Labeobarbus beso f1 63.4 28.2 9.3 0.0132* Labeobarbus beso c1 48.7 28.1 12.38 0.0568 Labeobarbus f2 77.8 45.5 8.41 0.0024* Labeobarbus c2 43.8 37.7 7.10 0.0910 intermedius intermedius Enteromius f2 27.3 18.4 8.82 0.2563 Enteromius c3 37.5 22.7 11.04 0.1694 yardiensis yardiensis Micropanchax f2 81.8 36.8 8.91 0.0024* Micropanchax c2 57.1 33.0 10.26 0.0150* antinorii antinorii Clarias gariepinus f2 100 41.6 8.56 0.0002* Clarias gariepinus c2 50.0 35.4 9.78 0.0230* Oreochromis f2 87.5 44.1 8.02 0.0008* Oreochromis c2 46.7 36.6 8.63 0.0452* niloticus niloticus Caddisflies Ecnomus nya t2 80.0 23.9 11.96 0.0072* Ecnomus nya c2 46.7 23.8 12.70 0.1424 Ecnomus similis t2 100.0 24.9 12.55 0.0004* Ecnomus similis c2 77.8 25.9 12.94 0.0136* Ecnomus thomasseti t4 20.0 24.1 12.31 0.5765 Ecnomus thomasseti c3 19.9 23.9 12.55 0.4493 Dipseudopsis t3 36.0 25.2 12.52 0.2000 Dipseudopsis c3 30.0 26.1 13.17 0.3065 capensis capensis Amphipsyche t3 45.7 27.7 10.68 0.0662 Amphipsyche c3 51.9 30.2 11.37 0.0656 senegalensis senegalensis Cheumatopsyche t1 45.5 29.1 9.83 0.1476 Cheumatopsyche c2 54.4 33.2 10.49 0.1248 afra afra Cheumatopsyche t3 45.5 30.6 7.59 0.0184* Cheumatopsyche c3 41.9 35.1 9.72 0.3185 columnata columnata Cheumatopsyche t2 31.0 29 9.86 0.5181 Cheumatopsyche c2 54.4 33.1 10.45 0.1218 falcifera falcifera Cheumatopsyche t1 50.0 28.8 10.02 0.0922 Cheumatopsyche c1 55.9 32.1 10.71 0.0778 massa massa Cheumatopsyche t2 20.0 22.3 5.07 1.0000 Cheumatopsyche c2 33.3 16.7 7.52 0.1686 sexfasciata sexfasciata Cheumatopsyche t1 33.3 22.2 4.96 0.1656 Cheumatopsyche c1 14.3 16.6 7.46 0.5567 themaz themaz Hydropsyche t2 20.0 22.1 4.89 1.0000 Hydropsyche c2 33.3 16.7 7.56 0.1702 abyssinica abyssinica Hydroptila cruciata t4 83.3 26.4 12.07 0.0020* Hydroptila cruciata c3 14.1 28.1 12.48 1.0000 Hydroptila sp. 4 20.0 22.2 4.92 1.0000 Hydroptila sp. c1 14.3 16.7 7.52 0.5529 Orthotrichia thariel t2 41.7 30.8 6.48 0.0170* Orthotrichia thariel c2 45.5 36.3 8.62 0.2118 Lepidostoma scotti t1 33.3 22.2 4.96 0.1656 Lepidostoma scotti c1 14.3 16.6 7.46 0.5567 Athripsodes fissus t2 20.0 22.2 4.97 1.0000 Athripsodes fissus c1 14.3 16.7 7.51 0.5533 Oecetis armaros t1 33.3 22.2 4.96 0.1656 Oecetis armaros c1 14.3 16.6 7.46 0.5567 Oecetis reticulatella t3 40.0 28.4 9.77 0.1522 Oecetis reticulatella c2 61.5 31.9 10.60 0.0088* Oecetis tripunctata t2 60.0 22.8 13.02 0.0434* Oecetis tripunctata c2 100.0 22.7 11.01 0.0016* Oecetis sp. t3 20.0 22.3 5.04 1.0000 Oecetis sp. c3 12.5 16.7 7.49 1.0000 Setodes squamosus t2 40.0 20.2 13.23 0.2216 Setodes squamosus c2 66.7 19.5 10.83 0.0196*

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Table 5 continued Species Zonea IV Mean SD P Species Zonea IV Mean SD P

Tagalopsyche t2 40.0 20.2 13.23 0.2216 Tagalopsyche c2 66.7 19.5 10.83 0.0196* aethiopica aethiopica Triaenodes serratus t2 60.0 22.8 13.02 0.0434* Triaenodes serratus c2 100.0 22.7 11.01 0.0016* Trichosetodes t2 40.0 20.2 13.23 0.2216 Trichosetodes c2 66.7 19.5 10.83 0.0196* tjonnelandi tjonnelandi Trichosetodes t3 20.0 22.3 5.05 1.0000 Trichosetodes c3 12.5 16.5 7.37 1.0000 truncatus truncatus Parasetodes sp. t3 83.3 26.5 11.97 0.0022* Parasetodes sp. c3 50.9 28.0 12.60 0.0550 Nyctiophylax t2 20.0 22.2 4.94 1.0000 Nyctiophylax c2 33.3 16.6 7.42 0.1620 armigera armigera *Significant at P \ 0.05 level aZones refer to those in Figs. 2, 3a intermedius, M. antinorii, C. gariepinus, and O. Discussion niloticus were indicative for river stretches down- stream of S6 and in tributaries T1 and T3 (Table 5). The objective of our study was to explore biotic Regarding caddisflies, we distinguished four dif- zonation patterns along the endorheic Awash River ferent zones. Lepidostoma scotti, C. themaz, and O. and its major tributaries in the dry season. By armaros were only recorded from the Chilimo Forest providing species-level information and using a com- (2,389 m) but were not found indicative for the entire bined approach of fish, adult caddisflies and environ- river stretch above 2,063 m (Table 5). Here, C. massa mental variables, we were able to assess the species’ was most characteristic. Sites S4–8 were distinguished longitudinal distribution patterns in this tropical river, by E. similis and E. nya, but also by several species of describe distinct fish and caddisfly assemblages, and the family Leptoceridae (Table 5). In the lowlands, detect indicator species relevant for river Parasetodes sp., C. columnata, and A. senegalensis management. were most indicative. In contrast to the main channel, tributaries (T1–3, T7) were best characterized by H. Biotic zonation patterns and indicator species cruciata. of the Awash River For the combined matrix of fish and caddisflies, our analyses revealed three zones with the following Our results show that fish and caddisfly assemblages in indicator species (Table 5): G. aethiopica, L. beso, the Awash River drainage split into two and four and C. massa were most indicative for the Upper separate groups, respectively. The combined analyses Awash (mainstem) and tributaries T2 and T7, sup- of both organism groups clearly distinguished the porting the individual analyses presented above. The species assemblages into highland and rift valley transition zone was best characterized by G. makien- communities, which are separated by an ecotone sis, L. intermedius, M. antinorii, C. gariepinus, O. (transition zone) with highest diversity between 1,200 niloticus, E. similis, Oecetis reticulatella, O. tripunc- and 1,600 m. These results would lead us to propose tata, S. squamosus, T. aethiopica, T. serratus, and T. three distinct biocoenotic zones for the Awash River. tjonnelandi. Based on the CA, all of the above fish However, our findings also indicate that the Upper species were found characteristic for the lowland Awash should be further subdivided into two sections, fauna (Fig. 3b). Their presence at an altitude of totalling four discrete zones of the mainstem river: the 1,608 m (S6) represents their upper distribution limit source region (1a), the Upper Awash (1b), a transition in the Awash River. For the Lower Awash River, the zone (2), and the Lower Awash (3) (Fig. 4). indicator analysis found Parasetodes sp. and A. senegalensis most characteristic, supporting the indi- vidual analysis for caddisflies.

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Zone 1a variables to separate the Upper Awash River from the lower zones. The Awash River’s source region, located in the Chilimo Forest ([ 2,389 m), is characterized by Zone 2 caddisflies as fish species (G. aethiopica, G. dem- beensis) were only present up to a small cascade The section between S6 and S8 (S9) constitutes a restricting further upstream distribution (Englmaier, transition zone between the upper and lower reaches of 2018). Three of the present caddisfly species (L. scotti, the Awash River. Similar to conclusions of other C. themaz, O. armaros), which so far are only known studies (e.g. Statzner & Higler, 1985; Thorp et al., from Ethiopia (Malicky & Graf, 2015; Terefe et al., 2006), our data showed that this ecotone offers a high 2018), exclusively occur at S1 in Chilimo Forest. The habitat variability (see Table 1), which is influenced headwater community consists of shredders (Lepidos- by Koka Reservoir and the natural lakes in the central toma) and predators (Leptoceridae: Oecetis). As these part of the Main Ethiopian Rift, and exhibits the species inhabit clear water sections over coarse highest species numbers, particularly of caddisflies. substrate and with lower (\ 16°C) water temperatures Hence, regarding indicator species, the transition zone (Table 1), they disappear in deforested areas down- is predominantly characterized by caddisflies such as stream with higher proportions of fine sediment (due E. similis, O. tripunctata, and T. serratus, which were to erosion), less input of coarse particulate organic three of the seven indicator caddisfly species for the matter, and an increase in water temperature. combined dataset. The fish species present in this zone are all members of the lowland fauna. The significant Zone 1b indicator values for fish in the combined dataset appear overestimated as G. makiensis, C. gariepinus, The Upper Awash River from S2 to S5 and M. antinorii have their upstream limit in this zone. (2,389–1,200 m) is more or less homogeneous regard- Interestingly, the distribution boundary of these fish ing fish; G. aethiopica and L. beso are characteristic species is consistent with the upstream limit of species for this reach. Whilst the former is omnivo- crocodiles (Cott & Pooley, 1972; Siege & Koch, rous, typically scraping off food particles from various 2017), which can be seen as equally indicative for substrates (Stiassny & Getahun, 2007), the latter is a zones 2–3. specialized scraping feeder associated with stony substrate (Levin, 2012); both are adapted to high flow Zone 3 velocities and cooler water temperatures (Golubtsov et al., 2002). The cascades at Awash Kunture consti- In the Lower Awash River (1,214–338 m), species tute a marked interruption in the river, affecting the diversity is lower than in the transition zone. Here, in upstream distribution of several other fish species. The the northern part of the Main Ethiopian Rift, water caddisflies of this section are widely distributed temperatures are consistently higher than upstream, throughout the highlands and already show a transition and conductivity measurements showed a large range. towards the rift valley communities; C. massa and C. The increase in conductivity between S9 and S10 afra are representatives for the Upper Awash zone. probably results from the influence of the saline Lake Except for the Chilimo Forest, the rest of the Ethiopian Beseka (conductivity [ 6,000 lScm-1; Goerner Highlands are under intense anthropogenic pressure et al., 2009), which flows into the Awash River due to deforestation and high livestock density (e.g. through an artificial channel. The environmental Kebede et al., 2020). Hence, although we propose that parameters most decisive for the community compo- the unique caddisfly fauna in the Chilimo Forest sition of zone 3 were conductivity, water temperature, represents a distinct section (zone 1a), the separation and fine-grained sediment (psammal and pelal). The of the Upper Awash might also be due to the extensive species assemblages typical to the rift valley start to loss of natural highland forests (Nyssen et al., 2015; occur downstream of S8 (S9 for fish assemblages) but Kebede et al., 2020). Overall, slope and mesolithal become marked after the gorge section at S10. In the substrate were the most decisive environmental Lower Awash River, G. makiensis and C. gariepinus, as well as A. senegalensis and C. columnata, are most 123 Hydrobiologia widespread. Garra makiensis is predominantly rheo- with high dispersal capacities managed to recolonize philic but capable of inhabiting limnetic habitats the Lower Awash River. Furthermore, it must be noted (Golubtsov et al., 2002). All fish species of the Lower that the river morphology of zone 3, which is Awash seem to tolerate high water temperatures with considerably shaped by the geotectonic history of the G. dembeensis showing the greatest amplitude Main Ethiopian Rift (Bonini et al., 2005; Abbate et al. (15.9–34.2°C) (Tables 1, 2). 2015), is characterized by alternating sections of The low number of indicator species for such a confined river stretches (including cataracts) and comparably long zone is surprising. The geographi- alluvial floodplains as well as low and steep gradients cally wide-spread community in the Lower Awash (Fig. 4). As such discontinuities within a similar zone River presumably results from a combination of may be of considerable ecological importance (Statz- different factors, such as geotectonics, water temper- ner & Higler, 1986), the densification of sampling sites ature, and alternating dry periods in the history of the (e.g. including floodplain water bodies) might expose Main Ethiopian Rift (Bonnefille et al., 2004; Sagri the presence of smaller patches ‘‘within a hierarchy of et al., 2008; Foerster et al., 2014; Benvenuti & larger spatiotemporal patches’’ (Thorp et al., 2006), Carnicelli, 2015). Regarding the latter, it is likely that possibly revealing a fauna distinct from the general parts of the Awash River fell dry in the past, thereby pattern of zone 3, which might go hand in hand with a causing species to become locally extinct. After re- repetition of smaller functional process zones along wetting, most-probably widely distributed species the river. However, according to the serial

Chilimo forest Gorge section upstream of Adayita Koka Reservoir Lake Gamari (a)

1,810 m a.s.l. 560 m a.s.l. 580 m a.s.l. 410 m a.s.l. Akaki R. Borkana R. (b) Yewuha R. 570 m a.s.l. Mille R. Robit R. Ataya R. Jara R. L. scotti** , C. themaz , O. armaros * Active floodplain width 2,389 G. aethiopica (schematic) 2,244 C. massa** , C. afra , L. beso Gorge section * Caddisfly species E. nya** , E. similis source region (1a) O. tripunctata** , T. serratus Upper Awash (1b) transition zone (2) N. armigera*, H. abyssinica*, S. squamosus** , T. aethiopica , T. tjonnelandi * Lower Awash (3) 1,608 L. intermedius O. thariel* G. makiensis, C. gariepinus, M. antinorii 1,214 D. capensis** , A. senegalensis , C. columnata** , O. reticulatella Parasetodes sp.*

Altitude (m a.s.l.) E. yardiensis G. dembeensis 1a 1b 2 3

338 014 205 328 1,250 Distance from source (km)

Fig. 4 Schematic representation of the longitudinal zonation of the Awash River, showing typical landscape forms, lateral (a) and longitudinal (b) river gradient, and characteristic fish and caddisfly species 123 Hydrobiologia

250 Melka Kuntu re Melka Hombole 200 below Koka dam

1 Wonji 3- 150

100

Discharge (m s ) 50

0 12345678910 11 12 Month

Fig. 5 Mean monthly flow magnitude measured at four below Koka Dam (8° 280 600 N, 39° 90 3300 E), Wonji (8° 280 2400 gauging stations on the Awash River—in downstream direction: N, 39° 120 4800E). Data source Ethiopian Ministry of Water, Melka Kunture (8° 420 1500 N, 38° 360 2200 E), Melka Hombole Irrigation and Electricity (2019) (8° 220 4500 N, 38° 460 4600 E; upstream of Koka Reservoir), discontinuity concept (Ward & Stanford, 1983, 1995), springs. Caddisfly assemblages tend to be similar to the influence of Koka Reservoir and the other the lowland communities, despite an impressive impoundments (see Fig. 1) may be another reason altitude range of the tributaries (482–1,902 m). Also, for the rather long and homogeneous Lower Awash fish assemblages show a similar pattern to the Lower River section. Not only do these dam structures disrupt Awash River, with the exception of T2 and T7, which the longitudinal river gradient and constitute a recent are associated to the Ethiopian Highlands. The indi- upstream dispersal barrier, but they also homogenize cator species of these streams, H. cruciata, is appar- the flow regime downstream of the reservoir (Fig. 5). ently associated with coarse substrate and high flow These flow regime modifications may have caused velocities, and is widely distributed throughout Africa changes within the community in the Lower Awash (Botosaneanu, 2002). River (e.g. Junk et al., 1989; Winemiller, 2004; Hayes Several authors have contributed observations from et al., 2018). Besides, the reservoirs may cause, for tropical rivers for fish (e.g. Ibanez et al., 2007;Arau´jo example, through plankton production (Degefu et al., et al., 2009; Payne et al., 2010; Fitzgerald et al., 2018) 2011), considerable alterations in the food resources and caddisflies (e.g. Malicky & Chantaramongkol, downstream. In the reservoir itself, the accumulation 1993; Chaibu, 2000; de Moor et al., 2000; de Moor, of fine sediments (Kropa´cˇek et al., 2016) may have 2011), but no common classification of stream implications for the aquatic fauna (Jones et al., 2007). sections into general zonation concepts has yet been achieved (Aarts & Nienhuis, 2003). This might be due Tributaries to the fact that the predictability of zonation patterns becomes more difficult above the ecoregional level The tributaries of the Northern Eastern Rift (T1–3, T7) (Thorp et al., 2006). In the Awash River, we found that exhibit a pattern distinctive of that from the mainstem species assemblages in the mainstem were mostly river zones. Their substrate composition is similar to distinct between the two ecoregions but were the same that of the Upper Awash, dominated by coarse gravel within a single ecoregion (with the exception of the to boulders. However, their riverbeds are much wider transition zone for the caddisfly dataset). Depending and the water temperatures are higher compared to the on the dataset used for the analyses, the tributaries— mainstem Awash River at similar altitudes (Table 1). located at the border of both ecoregions—were either In the Middle Borkana River (T3) and the Yewuha grouped with the lowland sites (combined and fish River (T6) water temperatures exceeded 30°C, which datasets) or showed a separate group (caddisfly is possibly linked to the presence of hot thermal dataset). Regarding the first, however, the assemblage

123 Hydrobiologia of the Upper Borkana River (T2) and Robit River (T7) for the widespread O. niloticus (Nilo-Sudan), C. was clustered with the Upper Awash River in the gariepinus (Pan-African), G. dembeensis (Nilo-Su- highlands. Nevertheless, it cannot be completely dan), and L. intermedius (Nilo-Sudan), the fish species elucidated if the grouping of sites resulted primarily are endemic to Ethiopia (Golubtsov et al., 2002;de from their location in the ecoregion or along a steep Graaf et al., 2007; Stiassny & Getahun, 2007; altitudinal gradient (however, one is not completely Englmaier et al., 2020). Indeed, it has been recognized independent of the other anyways). This raises the that the northern and central parts of the Main question if precise definitions of zones, such as Ethiopian Rift exhibit a fish species composition rhithron and potamon (Illies & Botosaneanu, 1963) distinct from the Nilo-Sudan ichthyofaunal province, are needed and applicable on a global scale (without with affinities to the freshwater ecoregions of the introducing several specific exceptions). Clearly Ethiopian Highlands and the Western Red Sea defined river sections might be applied individually Drainages (Roberts, 1975; Paugy, 2010). Characteris- depending on the local characteristics of the respective tic families for the Nilo-Sudan ichthyofauna (e.g. river. In general, the longitudinal river zonation of Characidae, Mochokidae, Mormyridae, Tetraodonti- biota depends on type, range and interaction of various dae) are absent from the Awash; others (e.g. Bagridae, environmental and/or biotic gradients (e.g. Hawkes, Claroteidae) are extinct (Stewart & Murray, 2017). 1975; Malicky & Chantaramongkol, 1993;Arau´jo Two species reported earlier from the Awash, E. et al., 2009). The stronger the gradient, the stronger the akakianus and Aphanius dispar (see Golubtsov et al., demarcation between biocoenoses will be, resulting in 2002), were not found in the present surveys. Their distinct zones or patches with more or less sharp current status needs clarification. transitions. Independent from geographic location and The highland fauna with G. aethiopica (morpho- faunal composition, more or less well separated logically close to G. quadrimaculata), G. dembeensis, species assemblages will be visible. and L. beso is similar to that of the Upper Blue Nile Overall, river zonation and measurements of asso- (Golubtsov et al., 2002). The genera Garra and ciated indicator species can provide vital information Labeobarbus are common in the headwaters of all to inform integrated river basin management (Lorenz Ethiopian drainages (Habteselassie, 2012). Con- et al., 2001). In this regard, knowledge on fish and versely, however, headwater groups found elsewhere caddisfly diversity, for example, can be used for in tropical or southern Africa including Afronema- ecological status assessments (e.g. Lakew & Moog, cheilus, Amphilius, Chiloglanis, Enteromius, Kneria 2015; Alemneh et al., 2019). or Parakneria (Balon & Stewart, 1983; Skelton, 2001; Bills et al., 2012; Prokofiev & Golubtsov, 2013; Insights into species diversity Schmidt, 2014) are absent from the Upper Awash. The Lower Awash is inhabited by widely dis- The present findings are one of the first studies to tributed generalists like O. niloticus, C. gariepinus, investigate the longitudinal zonation patterns of fish and L. intermedius. Others such as E. yardiensis, M. and caddisfly assemblages in the Afrotropical realm antinorii, and G. makiensis are highly specialized and on the species level. The following section, therefore, show affinities to the Nile drainage (Englmaier et al., discusses the findings from a biodiversity perspective. 2020), the central East African rift (Golubtsov et al., 2002) and the Arabian Peninsula (Englmaier et al., Fish fauna unpublished data) respectively.

In comparison to the adjacent Omo-Turkana (79 Caddisfly fauna species), Blue Nile (64 species), White Nile (106 species) and Wabe Shebelle (31 species) drainage Only 92 species (9 families) of caddisflies are known systems (Golubtsov & Mina, 2003), the fish diversity so far from Ethiopia (Tobias & Tobias, 2008; Terefe in the Awash was exceptionally low (11 species) (see et al., 2018; Morse, 2020). Given the higher diversity Golubtsov et al., 2002). Furthermore, our results show in South Africa (253 species; de Moor & Day, 2013) that the fish fauna is dominated by cyprinids of the and Madagascar (500 species; Benstead et al., 2003), genera Labeobarbus, Garra and Enteromius. Except the Ethiopian fauna appears to be either poorly 123 Hydrobiologia investigated (Terefe et al., 2018) or greatly impover- C. falcifera, C. massa, E. nya, and E. similis—are ished. We collected only 28 species (7 families) within more widely distributed throughout Africa and seem the entire Awash drainage, although nearly 1,250 km to be insensitive to the loss of natural forest cover. of the main river and seven tributaries were surveyed. Despite being characteristic for the Ethiopian High- Kimmins (1963), Malicky & Graf (2012, 2015) and lands, those species present a transition to the rift Terefe et al. (2018) reported 14 additional species, valley community. increasing the number to 42 species in the Awash Some species, such as O. tripunctata, T. serratus, S. drainage. However, this number is still low if squamosus, T. aethiopica, and T. tjonnelandi, occurred compared to other tropical rivers such as the Mae exclusively in the wetland area of Koka Reservoir. Klang Catchment (Northern Thailand) with 171 Here, the river morphology changes sharply and the species (Malicky & Chantaramongkol, 1993; Chaibu, area becomes comparably flat, the river slope and flow 2000; Chaibu et al., 2002; Malicky, 2014). velocity are reduced, fine sediment is deposited, and In the Awash catchment, species of the families filter feeders with ultra-fine nets (D. capensis, A. Hydropsychidae and Leptoceridae were most widely senegalensis) occur here for the first time. Indeed, encountered. These families make up nearly two thirds studies from lakes and reservoirs (Mosely, 1931; of all species. Most species in the Awash are Kimmins, 1963) suggest that T. aethiopica, S. representatives of the Afrotropical region. Some squamosus, T. tjonnelandi, and T. aethiopica prefer caddisfly species cover huge geographic areas, for limnetic habitats and fine substrates. Aside from these example, H. cruciata (Cape Verdes, South Africa, four species, Kimmins (1963) found six other species Madagascar, Arabian Peninsula), A. senegalensis in the area around Koka Reservoir: C. afra, C. (West Africa, Egypt to South Africa), D. capensis sexfasciata, H. abysinnica, D. capensis, E. similis and E. similis (West Africa, Ethiopia, South Africa), and A. senegalensis. As mentioned earlier, the section O. tripunctata (wide distribution; Portugal to Bali; around Koka Reservoir apparently represents an Malicky, 2005), or elements of Central Africa like E. ecotone where highland and lowland species overlap nya, N. armigera, O. reticulatella (Kjærandsen & and coexist. With 29 species currently known from the Andersen, 1997; Olah & Johanson, 2008; Morse, central part of the Main Ethiopian Rift, this river zone 2020). Others are, as far as known today, Ethiopian shows a high diversity for the region as it contains endemics, including L. scotti, O. thariel, O. armaros, elements from the adjacent freshwater ecoregions. H. abyssinica, C. massa, and C. themaz (Malicky & In the Lower Awash River, the number of caddisfly Graf, 2012, 2015; Terefe et al., 2018). species is reduced (comparable to fish); some species Characteristic species of higher elevations (Upper which occur around Koka Reservoir are distributed Awash, [ 1,608 m) are L. scotti, O. armaros, C. further downstream, indicating a considerable influ- themaz, C. afra, Cheumatopsyche falcifera, C. massa, ence of the reservoir. Members of the rift valley E. nya, and E. similis. Their distribution was, however, community with a slight overlap to the highlands not uniform. The first three species solely inhabited consist of O. reticulatella, D. capensis, A. senegalen- the river’s source region in Chilimo Forest (Terefe sis, and C. columnata. In this zone, the river alternately et al., 2018). They apparently disappear in deforested flows through confined reaches and extensive wet- areas as we did not record them further downstream or lands (Fig. 4). The smooth stream gradient is fre- in the upper sections of tributaries. Nevertheless, quently interrupted by cataracts, resulting in species diversity in the forested highland areas might associated changes in substrate composition from fine be higher than we recorded. Malicky & Graf (2015), to large substrates or bedrock. In stony sections, for example, described species such as Hellyethira including the tributaries in the Northern Main marioch, Stactobia ruthiel, Orthotrichia gudiel, and Ethiopian Rift, we found H. cruciata. Though faunal Athripsodes druchas from a small forest creek north of elements of the lowlands are comparable with other Addis Ababa. The genus Lepidostoma is a character- river systems in the Afrotropical region (e.g. Gibon & istic element of the highlands in several African Statzner, 1985; de Moor et al., 2000) the fauna in the regions (Mosely, 1939; Marlier, 1954). The other Awash River is largely impoverished. species peculiar for the Upper Awash region—C. afra,

123 Hydrobiologia

Drivers of diversity supports a rich fauna. Lake Abbe in the Afar Depression is highly saline and an extreme habitat Both, fish and caddisflies exhibited an exceptionally for fish and caddisflies. low diversity in the Awash River catchment. Reasons for the apparently low species numbers might be Climatic characteristics related to the following characteristics. The Awash drainage system is located in an area Anthropogenic impacts subject to extreme climatic conditions. It is distin- guished by high temperatures and exceptionally low The Awash River is under extreme human pressure. precipitation (Fazzini et al., 2015). In the Afar region, Deforestation, plantations of Eucalyptus and Prosopis, the high water temperatures might be a limiting factor intensive agricultural use and overgrazing by livestock for species distribution, potentially exceeding the linked with high nutrient input and erosional pro- ecological tolerance of several species. Paleoclimatic cesses, as well as industrial and domestic water and paleohydrological studies have shown frequent pollution, are common (Degefu et al., 2013; Keraga lake level changes in the Main Ethiopian Rift (Grove et al., 2019). However, this affects mainly the et al., 1975; Le Turdu et al., 1999; Sagri et al., 2008; highlands. In the Lower Awash River, livestock is Benvenuti & Carnicelli, 2015), suggesting a long reduced and agriculture is focused at some few history of unstable environmental conditions. During irrigated areas. Anthropogenic degradation might dry periods in the past, the Awash River possibly therefore be a reason for the low diversity in the turned ephemeral, thereby limiting faunal persistence. Ethiopian Highlands more so than in lowland areas. Regarding caddisflies, it seems likely that widely Studies of reference streams in near-natural environ- distributed species with high dispersal capacities and ments are not known from Ethiopia, and generally, broad ecological ranges managed to recolonize old studies on tropical caddisflies at species level along habitats. The specialized fauna of Chilimo Forest, in comparable stretches are rare (e.g. Chaibu et al., contrast, indicates that more stable environmental 2002). conditions persisted over longer periods.

Geotectonic activities Possible methodological limitations

Geological data give evidence for frequent tectonic We sampled fish and caddisflies over three different and volcanic activities in the history of the Main years and periods (at the start, middle and end of the Ethiopian Rift (Benvenuti et al., 2002; Abbate et al., dry season) (Table 1). Although this did not seem to 2015). These events presumably not only affected the influence our results, the effects of temperature or geomorphology and connectivity of the Paleo-Awash river flow could have influenced species detection. (Sagri et al., 2008) but also the distribution of fish Besides, we investigated species diversity during the species (Beshera & Harris, 2014; Englmaier et al., dry season only and thereby did not cover the aspect of 2020). Moreover, thermal springs may have consid- seasonality. Even though phenological investigations erable influence on the water temperature at higher in tropical streams indicate long flight periods for most altitudes (e.g. Middle Borkana River, 31.2°Cat caddisflies throughout the year (e.g. Malicky, 2019), 1,417 m), possibly also affecting species composition little is known about flight periods of African species. (Lamberti & Resh, 1985). Kimmins (1963) found A. senegalensis during March and April, and Mosely (1948) detected specimens in River network January and June. However, substantial knowledge gaps regarding seasonality remain. The same is true The Awash River is an endorheic drainage system, regarding diurnal activity. This might have increased lacking the marine/estuary ecotone. In contrast to the change of missing caddisfly species, for example, large endorheic drainages of Africa such as the Omo those which are only active late in the night or early in (Ethiopia) and the Chad rivers (Central Africa), the the morning, in addition to the fact that most sites were Awash does not flow into a large lake basin that only investigated once. Especially the fauna of 123 Hydrobiologia cataract sections in the Lower Awash needs to be Furthermore, we described the most indicative investigated in detail but sampling efforts were limited species for the biocoenoses along the mainstem river due to inhibited accessibility. as well as its tributaries. As species-specific bioindi- The best explanation for the species-poor situation cators are rare or absent in most of the Afrotropical of caddisflies in the Awash River is, however, the region, these results may constitute a fundamental general poverty of the Afrotropical caddisfly fauna as element for the management of the Awash River and a whole, which cannot be explained at the present state beyond. of knowledge. Exact numbers of species cannot be Compared to other drainage basins in Eastern given because of taxonomic uncertainty of described Africa, the Awash River is rather species poor, which species, and more new species await discovery. Many may result from various natural and anthropogenic widespread caddisfly genera or families are either factors. Nevertheless, the highland forests seem to be lacking in tropical Africa (e.g. Rhyacophilidae which centres of specialized caddisfly species with small- are present with hundreds of species in Asia and even scale distribution, and the Awash lowlands harbour non-tropical Europe, or the genus Psychomyia with endemic fish species restricted to the Main Ethiopian well over 70 species in tropical Asia) or represented Rift. only by very few species (e.g. 1 species of Stenopsy- Possible limitations to our study include the aspects che, as compared to more than 50 only in western of sampling timing and lack of seasonality, which may China). Except for some species-poor endemic fam- have oversimplified our results. More studies are ilies or genera in southern Africa (Scott 1986, 1993), needed to understand spatio-temporal effects in only a few widespread species-rich genera are well distribution patterns in the Afrotropical region. represented in tropical Africa such as Leptoceridae, In summary, we found that a combined approach of Ecnomus, Cheumatopsyche, Chimarra,orDipseudop- fish and caddisflies proved to be a suitable method for sis. Rivers in Asia and Europe contain by far more identifying longitudinal and regional characteristics of species than the Awash River. For example, 91 species fluvial ecosystems in tropical environments. In the are reported for the Mae Nam Ping in Thailand over a future, East African research must focus on taxonomy, stretch of 120 km (Chaibu & Chantaramongkol, 1999; ecology and distribution patterns on species level. Chaibu, 2000; Chaibu et al., 2002; Malicky, 2014), 98 Such investigations are urgently needed to foster the species for the Drava River at the border between development of reliable systems for assessing and Hungary and Croatia (Uherkovich & No´gra´di, 2018), monitoring the integrity of tropical river systems and 81 species in the Po River in Italy (Bertuetti et al., their biodiversity. 2001), or 61 species in the middle part of Danube River in Central Europe (Malicky, 2014). Acknowledgements Fieldwork was conducted under the auspices of the LARIMA Project (Project Number 106) funded by the Austrian Partnership Programme in Higher Education and Research for Development (APPEAR) of the Conclusion Austrian Development Cooperation (ADC) and the Austrian Agency for International Cooperation in Education and Our study showed that, in the tropical endorheic Research (OeAD). Field research was supported by the National Fisheries and Aquatic Life Research Center Awash River, fish and caddisfly assemblages sampled (NFALRC) and the Ethiopian Institute of Agricultural during the dry season are clearly clustered into Research (EIAR) (Permit Numbers 1.9/0323/2017, 1.9/3196/ highland (Upper Awash) and rift valley (Lower 2018, 1.9/0336/2019). G.K.E. was supported by a Grant from Awash) communities, separated by an ecotone (tran- the Doctoral Academy Graz, Ecology and Evolution in Changing Environments (EECE), University Graz. D.S.H. sition zone) with highest species diversity. The fish benefited from a Ph.D. Grant sponsored by Fundac¸a˜o para a and caddisfly assemblages are congruent in their Cieˆncia e a Tecnologia I.P. (FCT), Portugal (PD/BD/114440/ overall distribution patterns, which reflect changes in 2016). CEF is a research unit funded by FCT (UID/AGR/00239/ altitude and jumps between ecoregions. Only caddis- 2013). We are thankful to the staff members of Ambo University and the National Fisheries and Aquatic Life Research Centre, flies exhibited a narrower niche in the headwaters, Sebeta for providing logistics during field work. Asefa Keneni, separating the Upper Awash River into a forested and Moges Kidane Biru (Ambo University), and Gerold Winkler a deforested zone. (IPGL, BOKU-Vienna) provided valuable comments and support to the study. The invaluable taxonomical assistance of

123 Hydrobiologia

Franc¸ois-Marie Gibon (Olemps, France) is appreciated. We and some concepts in river ecology. Hydrobiologia 618: thank the local communities along the Awash River for 89–107. providing access to the sampling localities. Balian, E. V., H. Segers, C. Le´veˆque & K. Martens, 2008. The Freshwater Animal Diversity Assessment: an overview of Data availability Data are available from the corresponding the results. Hydrobiologia 595: 627–637. authors upon reasonable request. Balon, E. K. & D. J. Stewart, 1983. Fish assemblages in a river with unusual gradient (Luongo, Africa: Zaire system), Compliance with ethical standards reflections on river zonation, and description of another new species. Environmental Biology of Fishes 9: 225–252. Conflict of interest The authors declare no conflict of interest. Benstead, J. P., P. H. De Rham, J. L. Gattolliat, F. M. Gibon, P. V. Loiselle, M. Sartori, J. S. Sparks & M. L. J. Stiassny, Open Access This article is licensed under a Creative Com- 2003. Conserving Madagascar’s freshwater biodiversity. mons Attribution 4.0 International License, which permits use, BioScience 53: 1101–1111. sharing, adaptation, distribution and reproduction in any med- Benvenuti, M. & S. Carnicelli, 2015. The geomorphology of the ium or format, as long as you give appropriate credit to the lake region (Main Ethiopian Rift): the record of paleohy- original author(s) and the source, provide a link to the Creative drological and paleoclimatic events in an active volcano- Commons licence, and indicate if changes were made. The tectonic setting. In Billi, P. (ed.), Landscapes and Land- images or other third party material in this article are included in forms of Ethiopia, World Geomorphological Landscapes. the article’s Creative Commons licence, unless indicated Springer, Dordrecht: 289–305. otherwise in a credit line to the material. If material is not Benvenuti, M., S. Carnicelli, G. Belluomini, N. Dainelli, S. 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